Development has hitherto been made on a technology for an assembled battery that is aimed at increasing an amount of power that can be stored in the assembled battery and reducing loss during charge and discharge by combining power storage elements in series.
In order to eliminate a voltage variation among individual power storage elements caused by an individual variation of the power storage elements when the power storage elements are connected in series to supply electric power to a vehicle, it is necessary for the assembled battery that the power storage element be provided with a discharge circuit (cell balancer) and the discharge circuit be driven intermittently during a stop of the vehicle to maintain a voltage balance of the power storage elements.
When a malfunction occurs in a discharge switch or a voltage drop element included in the discharge circuit, however, there is a problem in that a voltage balance among the power storage elements is lost and a power storage element is overcharged or overdischarged.
To deal with this problem, there is proposed an assembled battery discharge device, including a discharge circuit, which is formed of one or more voltage drop elements and a discharge switch connected in series, and which is configured to discharge each secondary battery (cell) serving as a battery constructing an assembled battery, to thereby reduce a voltage variation among the secondary batteries of the assembled battery, a voltage detection circuit configured to detect a terminal voltage of the secondary battery via the voltage drop element and not detecting the voltage of the secondary battery without the voltage drop element, and a discharge circuit malfunction determination section configured to determine a malfunction of the discharge circuit based on a difference between the terminal voltage generated when the discharge switch is turned on and the terminal voltage generated when the discharge switch is turned off, which are detected in time sequence, or based on a magnitude relationship of a ratio therebetween (see, for example, Patent Literature 1).
In this assembled battery discharge device, the discharge circuit malfunction determination section determines a malfunction of the discharge circuit based on the difference between the terminal voltage generated when the discharge switch is turned on and the terminal voltage generated when the discharge switch is turned off, which are detected in time sequence, or based on the magnitude relationship of the ratio therebetween. Thus, a malfunction of the discharge circuit can be detected with a simple configuration.